Coating of small particulates, commonly known as cores, beads, crystals, pellets, granules or seeds, is well known for creating spherical particles, such as pharmaceuticals. The typical size for such particles is 50-10,000 microns. The coating material is normally a polymer, which may be a copolymer or monomer. A rotor processor is commonly used for such coating. This processor has a cylindrical stator chamber with a rotatable disc mounted therein, and a narrow annular slit between the inner wall of the stator and the perimeter edge of the rotor. The rotor forms a floor in the chamber upon which particles are supported. The width of the slit is sufficiently narrow so as to prevent particles in the chamber from falling through the slit. Rotation of the rotor imparts centrifugal force to the particles, which are thrown to the wall of the stator, wherein air forced upwardly through the slit lifts the particles upwardly. The width of the slit governs the air velocity for a given air flow, which creates an upward draft which carries the particles upwardly. The upward movement of the particles continues, as long as the air velocity exceeds the transport velocity required to fluidize the particles. The air passing through the slit has a relatively high velocity, and then expands into the larger volume of the chamber, thereby losing velocity. As the particles lose their transport velocity, they fall back toward the center of the rotor and return to the rotor surface. Thus, the rotating rotor and the upwardly flowing air create a circulating bed of particles within the chamber.
The particles are coated or layered during circulation through the bed. In the conventional layering process, a polymer, copolymer or monomer is dissolved in a solvent, which is then sprayed onto the particles in the chamber while the particles are circulating. The airflow also functions to dry the solution on the cores, with the layer thickness being built up as the particles continue circulating through the bed for repeated exposure to the sprayed solution.
Some polymers have an adhesive nature. In prior art coating processes, these polymers generally are diluted to 2-15% solids content to minimize agglomeration due to the adhesive nature. Furthermore, glidants are normally suspended in the polymer spray solution/dispersion so as to prevent or inhibit agglomeration during the coating process. Examples of glidants include titanium dioxide, calcium carbonate, magnesium stearate or any metal stearate, fumed or colloidal silica, sodium lauryl sulfate, graphite or any other finely divided material capable of reducing the adhesive nature of some polymers. Such glidants normally must be added to the polymer spray solution/dispersion in concentrations of 5-100%, based on the polymer solids in the solution/dispersion. These suspensions must be continuously agitated to prevent settling. The glidants in solution/dispersion often cause buildup in the spray guns, and thus blockage during processing, as well as problems with settlement in the solution/dispersion lines and other flow problems leading to inconsistent delivery during the coating process.
With the conventional polymer layering process, the polymers must be soluble so as to dissolve in a suitable solvent so as to be applied as a dilute liquid. Typical soluble polymers will be 5-15% solids in solution, by weight. In a pharmaceutical application, the polymers may function for modified release of active ingredients and/or for taste masking. In this type of application, polymers may be layered on the cores for 5-25% weight gain. In the case of organic solvent soluble polymers, as much as 5 kg of solvent must be used for each 1 kg of product coated. In scaled production, this is a very large amount of solvent per coated batch. For example, in a 5 kg batch of cores coated to a 25% weight gain with a 5% solids solution, a 25 kg solution is required, with the polymer application being approximately 2.5 grams of polymer substances per minute. Thus, the conventional layering process with dissolved polymers in solvent solution is slow and requires large volumes of solvents.
In the conventional rotor processors, such as the GX or GXR sold by Applicant, the expansion chamber of the processor is normally maintained at a slightly negative pressure. Pulse filters are provided at the top of the processor and are connected to a positive compressed air source. The product powder port is located above the rotor chamber to drop powder downwardly by gravity and/or pulled into the processor by the negative internal pressure onto the circulating particles. The powder port is an opening without a closure or seal. Occasionally, the filter pressure may exceed the chamber pressure, in which case the powders are forced out of the open powder port. Some powders are toxic, which presents a hazardous situation. Also, the loss of powder from the processor is a wasteful cost.
Accordingly, a primary objective of the present invention is the provision of an improved rotor processor for supplying dry powder polymers or glidants to the particle bed in the rotor chamber.
Another objective of the present invention is the provision of an improved powder feed system for a rotor processor which introduces dry powders into the rotor chamber for application to particles in the circulating bed.
A further objective of the present invention is the provision of an improved rotor processor having a powder feed system with a precise screw conveyor, and eductor, and a ball mounted powder conduit.
Still another objective of the present invention is the provision of an improved rotor processor wherein dry powders are introduced into the rotor chamber at a level circumferentially spaced from the liquid spray gun of the rotor chamber.
Yet another objective of the present invention is the provision of an improved rotor processor having separate spray and powder zones in the rotor processor through which circulating particles sequentially and repeatedly pass.
A further objective of the present invention is the provision of an improved rotor processor for dry powders which introduces the powders into the rotor chamber under a positive pressure.
Another objective of the present invention is the provision of an improved rotor processor for application of dry powders to the circulating particle bed which is effective and efficient.
These and other objectives will become apparent from the following description of the invention.